Destearinization of glyceride oils



Patented May 18, 1954 DESTEARINIZATION OF .GLYCERIDE OILS Elmer W. Brennan, Carpentersville, Paul R. Chapman, Lake Zurich, and GeorgeWolfram, Union, 111., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application September 21, 1951, SerialLNo. 247,764

This invention relates to the separation of cer tain constituents from liquid mixtures. of glyceryl ester. of high molecular weight fatty acids. More specifically, the invention is concerned with improving the low temperature characteristics of glyceride oils.

Animal, vegetable and fish and marinesanimal oils have long been available as valuable articles of commerce. These oils in their natural state consist chiefly of mixtures of neutral glyoerides of unsaturated and saturated fatty acids. Although there are numerous applications in which these mixtures of saturated and unsaturatedglycerides may be employed, in some applications their mutual incompatibilities will not provide desired results. For example, it is well known that certain types of fatty oils are employed as drying agents in various types of paints. Themechanism of these drying oils depends upon the unsaturation of the various constituents of the drying oils and if saturated materials are present the efficiency of the drying oil is affected, Likewise fatty oils provide natural raw materials for the productionof fatty acids. When the fatty oil is hydrolyzed to produce a mixture of fatty acids and glycerine, it isirequently desirable to separate the saturated acids from the unsaturatediatty acids. Another important application in which fatty oils are employed is in the production of lubricating oil additives. rated materials with suliurization agents, fatty oils having a high content of unsaturated constituents are very usefully employed in preparing sulfurized lubricating oil additive agents. One of the most important functions of sulfurized fatty oils is in the "preparation of E. P. additives. These additives when admixed with a suitablemineral oil base enhance the inherent lubricity properties of mineral oils. An important use of such sulfurcontaining mineral oil compositions is in gear oils which are employed as lubricants in automotive hypoids, and other gears and transmissions found in automotive vehicles. Among other requirements it is essential that the compounded gear oil have suificient fluidity. This fluidity is determined by subjecting the oil to the so-called channelling test. This test, which is described in detail in C. R. C. Handbook, Coordinating Research Council (1946) at page 452, is used in determining the channelling characteristics of universal gear lubricants at low temperatures. In essence the test consists of drawing ametal strip, held vertically with the flat end in contact. with thebottom of-a. container holdingthe oilsample, across the bottomoi the container and measuring-the time Because of the high reactivity of unsatuit takes to completely reconceal the 'bottomof the container by the lubricant. The test is essentially a determination of the fluidity of a lubricant and is directly related to the pour point of the various constituents which comprise the compounded'gear oil. The channel test requirements vary for different grade of gear oils. It is recommended that grade gear oil have a 0 F. channel, while -50 F. is recommended for the '75 grade oil. While there is no direct relationship or function between the pour point of a fatty oil raw material used in the preparation of sulfurized E, P. additives, the pour point of the fatty oil may influence the pour point of the final blended product. For example, a finished lubricant formulated with an additive component prepared from a lard oil having a +45 F. pour point would have a 0 to a +5 F. pour point. Another finished lubricant using the same mineral oil base but formulated with an additive prepared from glyceryl trioleate having a pour point of +25 F. would have a pour point of 15 to -20 F. Therefore to preclude the possibility of adverse effect on the pour point of the compounded lubricating fluid, it is advisable to select judiciously, wherever possible, additive components having low pour points. Fatty oils generally employed in the preparation of sulfurized gear oil additives frequently do not possess a desirable low pour point and it is necessary to treat the fatty oil raw material prior to its being sulfurized to attain this objective.

The improvement of the low temperature characteristics of fatty oils is well known and is fre-'- quently termed destearinization for it is the removal of the stearins'which are the glyceryl'esters of stearic acid as well as other high melting point esters which brings about this improvement. These particular esters have relatively high melting points which detrimentally affect the pour point of the fatty oil. It is therefore necessary that their removal from the fatty oil raw material be effected. The destearinization of fatty oils in most instances involves the processing of the fatty oil at a low temperature to fractionally crystallize the steal-ins causing them to precipitate. These precipitant stearins are then removed by filtrationv leaving a mixture of glycerides which have improved pour point characteristics. Various modifications and improvements in this fractional crystallization have been effected by employing various types of solvents or manipulative processes for improving the cold test properties of afatty oil. These prior art methods are generally found to be satisfactory in processing edible oils which are used in the preparation of salad-oils.

In salad oil it is only necessary, relative to its low temperature properties, that under the normal storage conditions at temperatures between 40 and 50 F. there will be no precipitation of high pour materials. However, when fatty oils are used as reactants in the preparation of lubricating oil additives it is necessary that the fatty oil have a much lower pour point than the fatty oils employed in salad oils for this characteristic, while not having a direct relationship to the pour point of the blended composition, may have an influence on the pour point of the finished lubricant. It has been found that the known methods for destearinizing a fatty oil have not provided a material which will have a sufliciently low pour point to permit its use in the preparation of lubricating oil additives.

It is therefore an object of this invention to provide a method of fractional crystallization whereby a fatty oil is destearinized to produce a fatty oil material having improved low temperature characteristics.

Another object is to provide a method for destearinizing a lard oil to produce a raw material which may be satisfactorily employed When sulfurized as a gear oil additive agent.

In accordance with this invention it has been found that if a satisfactory low pour point fatty oil is to be obtained it is necessary to subject the fatty oil of high pour point, containing both high and low pour point glycerides, to a single stage, plural step chilling process. In this process the fatty oil raw material is initially dissolved in a suitable solvent. This solution is then chilled to a temperature of about 15 F. The mixture is maintained at this temperature for about 65 hours. At this time the temperature of the chilled mixture is reduced to about F. and maintained at this temperature for about 5 hours. The precipitated stearins are then removed by filtering or some other mechanical means, such as centrifuging, decanting, etc., and the acetone soluble material recovered. When this procedure or its equivalent is carried out it will be found that a destearinized fatty oil having substantially improved low temperature characteristics will be obtained.

It can be reasonably assumed that the lower the temperature at which destearinization is conducted the lower will be the pour point of the product obtained. In United States Patent 2,228,040 to Voogt, et al. a single stage process for refining a fatty oil to produce a low cold test oil is described. While the invention described in this patent substantiates the foregoing statement it has been found that the removal of the higher melting components of the fatty oil by this single step chilling method does not provide a material having a sufiiciently low enough pour point to permit the use of this material when sulfurized as an additive agent in a gear oil composition. In other words, it has been found that it is not the temperature alone which is the important element of the destearinization process but a combination of a plurality of cooling steps and proper temperature range are essential factors. By this expedient it is thought that a gradual precipitation of the more saturated glycerides is permitted, thereby yielding crystals of relatively large size that will not occlude the solvent solution.

To illustrate the instant invention several destearinizations of lard oils were carried out at various decremental temperatures. In carrying out this destearinization separate samples consistin of a lard oil-acetone solution were chilled to the test temperature and held at that temperature for 72 hours. The resulting mixture was filtered and the acetone-soluble portion recovered. The degree of destearinization was determined by the pour point of the acetone-soluble portion. The results of these tests are shown in Table I.

From the foregoing tabular summary it is seen that when a single stage, single step chilling process is carried out there is no appreciable improvement in the pour point of the destearinized material and in one instan c it is seen that when the destearinization was carried out at a temperature of 0 F. the pour point or the acetone soluble material was higher than the pour point of the original sample. The instant invention however provides a method for producing a low pour point material by means of destearinization in which the fractional crystallization is carried out by means of a single stage, plural step chilling operation. This procdure is shown by the following illustrative examples.

Emample 1.3061 grams of lard oil having an A. S. T. M. pour point of +40 F. and containing a small percentage of polyunsaturated materials were diluted with acetone in the ratio of 1 volume of lard oil to 5 volumes of acetone. This solution was then placed in a refrigerator. The solution was chilled to +15 F. and maintained at this temperature for 64 hours. It was then placed in another refrigerator and further chilled to a temperature of 0 F. and held at this temperature for 5 hours. The precipitated steari'ns were removed by filtration at the final destearinization temperature. A yield of 33% of acetone soluble material having an A. S. T. M. pour point of +15 F. was obtained.

Example 2.-By repeating the processing steps outlined in Example 1 a material having an A. S. T. M. pour point of +20 F. was obtained.

A comparison of these examples with the results summarized in Table I will show that the plural chilling cycle in which controlled rates of cooling and temperatures are used is essential to producing a low pour point fatty oil.

While it is not intended that this invention be limited by any theory of operation, the data obtained indicates the possibility of the formation and presence of eutectic mixtures. Another explanation of the instant invention is that when destearinization is conducted by means of a single stage, one-step process, such as described by Voogt, et al., rapid crystallization the acetone insoluble material occurs. This rapid crystallization results in the occlusion in the precipitate of solvent-soluble material having a pour-depressing effect thus producing a relatively high pour point filtrate.

The fractional crystallization which is carried out by the present invention can be obtained by using any solvent for fatty oils which is selective at low temperature for the non-stearin constitaerate? uents of the oil but which will not prevent the crystallization of the high melting point constituents at the temperatures employed in the process. Solvents such as acetone, methyl ethyl ketone, methyl or ethyl alcohols, paraffin hydrocarbons such as propane or hexane or Various substituted. hydrocarbons have a satisfactory solvent action. Of the foregoing, acetone is the preferred solvent when lard oils are being treated to produce a low cold test product. The solvent ratios employed in the foregoing illustrative examples were selected for convenience. It is to be understood that other ratios of solvent fatty oil may be employed depending upon the type of solvent and fatty oil material used. Ratios of 1 to 20 volumes of solvent to 1 volume of fatty oil may be used. Ordinarily, suiiicient solvent should be used to produce a homogeneous mixture or solution of solvent and. fatty oil under atmospheric conditions. The fatty oils which may be treated to improve their low temperature characteristics include in addition to lard oil, cottonseed oil, palm oil, whale oil, etc.

While it is seen from Example 1 above that a chilling cycle involving an initial chilling of the fatty oil solution to F. and a final chilling step conducted at 0 F., and a time element of 64 hours and 5 hours, respectively, the results produced by this invention may be obtained by initially chilling the fatty oil solution to a term perature between F. and 15 F. and thereafter chilling the initially chilled mixture to a ternperature between about 15 F. and 0 F. In general the temperature in the second chilling step will be approximately 15 F. below that of the initial step. The rate at which chilling takes place is not important but it is essential that the chilled solution be allowed to remain at the desired temperature after each chilling step for a period of not less than 5 hours. It is preferred however to maintain the solution at the first chilling temperature for a considerably longer period as, for example, 24 to 100 hours. It is necessary to maintain the fatty oil solution at the initial chilling temperature until substantially all of the stearins and other similar undesirable high melting point constituents which will crystallize and precipitate at that tempera ture are removed from the solution. It has been found that substantial proportions are removed from a solution at temperatures between about 5 F. to 30 F. The combination of time and temperature employed will, of course, depend upon the type and concentration of the high melting point constituents which are to be removed from original fatty oil material.

For example, processing a neats-foot oil which normally contains about 18% of palmitic acid and 3% stearic acid in the form of glycerides of these acids would require a less severe treating cycle than when refining a mutton tallow which contains about 25% of palmitic acid and of stearic acid in the form of glycerides. It is only necessary that at initial chilling temperature employed, a time element be used which will assure a substantially complete precipitation of those high melting point constituents which will crystallize out at that temperature. The length of time for the final chilling is similarly determined, that is a time sufficient for the crystallize. tion and precipitation 'of substantially the remaining high melting point materials which will precipitate at that temperature. Further more, when processing a fatty oil to obtain a product which will have improved low temperature characteristics and a high concentration of unsaturated constituents those low temperatures at which incipient crystallization and precipita tion of the unsaturated materials occur is obviously to be avoided.

It is therefore seen that in order to separate and remove the high melting constituents of a fatty oil to provide a material having good low temperature characteristics it is necessary that a plural chilling operation described by the instant invention be carried out. This method is necessary in order to prepare a fatty oil having a low enough pour point to permit its utilization, when further sulfurized, in a gear oil composition.

While the foregoing description has been confined to the destearinization of lard oils it is also intended that this invention include the separation of other high melting fats. Also, the term fatty oil in the appended claims and foregoing specification is meant to include vegetable oils, animal fats and oils, and marine animal fats and oils which contain high melting point constituents.

We claim:

1. In a process for improving the low temperature characteristics of a fatty oil containing high melting point esters of saturated fatty acids, the steps which comprise dissolving said fatty oil in a selective solvent for the desired constit uents of the oil, initially chilling the resulting fatty oil solution to a temperature not below about +5 F. at which a substantial proportion of the high melting point saturated fatty acid esters will crystallize and precipitate out of solution, maintaining said solution at this temperature for a time sufficient to precipitate out of solution a substantial proportion of said high melting point saturated fatty acid esters, further cooling the resulting mixture to a temperature not less than about 15 cooler than the initial chilling temperature, maintaining the ture at this temperature for a time sufficient to crystalline and precipitate out of the remaining solution additional amounts of the high melting point saturated fatty acid esters, separating solids and liquids and evaporating the solvent from the resulting liquid to recover a fatty oil material having a substantially decreased A. S. T. M. pour point.

2. A method for removing the high melting point constituents of fatty oils which comprises dissolving the said fatty oil in a selective solvent, initially chilling the fatty oil to a temperature of about +15 R, maintaining the said solution at this temperature for a time sufficient to crystalhas and precipitate out of solution a substantial proportion of said high melting point constituents, further cooling the resulting mixture to a temperature not less than 15 F. cooler than the initial chilling temperature, maintaining the said mixture at this temperature for a time sufficient to crystallize and precipitate out of the remaining solution an additional proportion of said high melting point constituents, separating the constituents of the resulting mixture at this latter temperature, and evaporating the solvent from the filtrate produced by said filtering to recover a fatty oil material having a substantially decreased A. S. T. M. pour point.

3. A method for removing the high melting constituents of fatty oils which comprises dissolving said fatty oil in a selective solvent, initially chilling the resulting fatty oil solution to a temperature not less than about +5 F. at which a substantial proportion of the high melting point constituents will crystallize and precipitate out of solution, maintaining said resulting mixture at this temperature for a time not less than about 5 hours to precipitate out of solution a substantial proportion of said high melting constituents, further cooling the resulting mixture to a temperature not less than 15 F. cooler than the initial chilling temperature, maintaining the said mixture at this temperature for not less than 5 hours to crystallize and precipitate out of solution the additional proportions of the high melting constituents, separating the constituents of the resulting mixture at this latter temperature, and evaporating the solvent from the filtrate produced by said filtering to recover a fatty oil material having a substantially decreased A. S. T. M. pour point.

4. A method for removing high melting constituents of fatty oils which comprises dissolving said fatty oil in a selective solvent, initially chilling the fatty oil to about +15 FE, maintaining said solution at this temperature for not less than 5 hours to precipitate out of solution a substantial proportion of said high melting point constituents, further cooling the resulting mixture to a temperature not less than 15 F. cooler than the initial chilling temperature, maintaining the said mixture at this temperature for not less than 5 hours to crystallize and precipitate out of the remaining solution additional proportions of high melting point constituents, separating the resulting mixture at this latter temperature, and evaporating the solvent from the filtrate produced by said filtering to recover a fatty oil material having a substantially decreased A. S. T. M. pour point.

5. A method in accordance with claim 4 in which the fatty oil is lard oil.

6. A method in accordance with claim 5 in which the selective solvent is acetone.

7. In a process for improving the low temperature characteristics of a fatty oil containing high melting point esters of saturated fatty acids the steps which comprise dissolving said fatty oil in a selective solvent, initially chilling the resulting fatty oil solution to a temperature not less than +5 F. at which a substantial proportion of the high melting point saturated fatty acid esters will crystallize and precipitate out of solution, maintaining said solution at this temperature for a 8 time sufficient to precipitate out of solution a sub stantial proportion of said high melting point saturated fatty acid esters, further cooling the resulting mixture to a temperature not less than 15 F. cooler than the initial chilling temperature, maintaining the said mixture at this temperature for a time sufficient to crystallize and precipitate out of solution additional proportions of the high melting point saturated fatty acid esters, the temperatures employed in the aforementioned chilling steps being above that temperature at which substantial amounts of the un saturated constituents of the said fatty oil will crystallize and precipitate out of solution, sep- T arating the resulting mixture at this latter temperature, and evaporating the solvent from the filtrate produced by said filtering to recover a fatty oil material having a substantially decreased A. S. T, M. pour point.

8. A method for removing the high melting point saturated fatt acid esters from a lard oil having a low content of fatty esters containing polyethenoid linkages, the steps which comprise initially dissolving said lard oil in acetone, initially chilling the lard oil solution to about +15 maintaining said lard oil at this temperature for not less than 5 hours, further cooling the resulting mixture to 0 F. and maintaining said solution at this temperature for not less than 5 hours, filtering the resulting mixture at 0 F. and evaporating the solvent from the filtrate produced by said filtering to recover a fatty oil material having a substantially decreased A. S. T. M. pour point,

9. A method in accordance with claim 8 in which the proportions of acetone and lard oil employed. are in the ratio of about 5:1.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,974,542 Parkhurst Sept. 25, 1934 2,450,235 Gee Sept. 28, 1948 2,514,608 Muckerheide July 11, 1950 2,619,421 Greenfield Nov. 25, 1952 FOREIGN PATENTS Number Country Date 555,570 Great Britain Aug. 30, 1943 

1. IN A PROCESS FOR IMPROVING THE LOW TEMPERATURE CHARACTERISTICS OF A FATTY OIL CONTAINING HIGH MELTING POINT ESTERS OF SATURATED FATTY ACIDS, THE STEPS WHICH COMPRISE DISSOLVING SAID FATTY OIL IN A SELECTIVE SOLVENT FOR THE DESIRED CONSTITUENTS OF THE OIL, INITIALLY CHILLING THE RESULTING FATTY OIL SOLUTION TO A TEMPERATURE NOT BELOW ABOUT +5* F. AT WHICH A SUBSTANTIAL PROPORTION OF THE HIGH MELTING POINT SATURATED FATTY ACID ESTERS WILL CRYSTALLIZE AND PRECIPITATE OUT OF SOLUTION, MAINTAINING SAID SOLUTION AT THIS TEMPERATURE FOR A TIME SUFFICIENT TO PRECIPITATE OUT OF SOLUTION A SUBSTANTIAL PROPORTION OF SAID HIGH MELTING POINT SATURATED FATTY ACID ESTERS, FURTHER COOLING THE RESULTING MIXTURE TO A TEMPERATURE NOT LESS THAN ABOUT 15* COOLER THAN THE INITIAL CHILLING TEMPERATURE, MAINTAINING THE SAID MIXTURE AT THIS TEMPERATURE FOR A TIME SUFFICIENT TO CRYSTALLIZE AND PRECIPITATE OUT OF THE REMAINING SOLUTION ADDITIONAL AMOUNTS OF THE HIGH MELTING POINT SATURATED FATTY ACID ESTERS, SEPARATING SOLIDS AND LIQUIDS AND EVAPORATING THE SOLVENT FROM THE RESULTING LIQUID TO RECOVER A FATTY OIL MATERIAL HAVING A SUBSTANTIALLY DECREASED A. S. T. M. POUR POINT. 